How to embed an integer in a macro string?

Question

My first time seeing stringification and token pasting. I feel like it could be a good tool for this macro:

#define MY_NUMBER   3
#define MY_STRING   "the number three: ##MY_NUMBER"
printf("%s\n", MY_STRING);

should output:

the number three: 3

What's wrong with `printf("%s %d\n", MY_STRING, MY_NUMBER)`??? — barak manos, Sep 01 '15 at 17:33
The printf is just for testing. The real question is meant to be creating the macro. — tarabyte, Sep 01 '15 at 17:39
Preprocessor operators (# and ##) do not work inside quoted string literals. You cannot use token concatenation to concatenate string literals, either; only individual tokens. (However, you can concatenate two string literals by just writing them one after another: `"Hello, " "world!"`). And finally, you can only use the stringify operator (#) on macro parameters. @alk: The linked answer is good but I fear that it is not really an answer to this confusion. — rici, Sep 01 '15 at 17:48

score 2 · Accepted Answer · answered Sep 01 '15 at 17:35

2

try this

#define S_(x) #x
#define S(x) S_(x)

#define MY_NUMBER   3
#define MY_STRING   "the number three: " S(MY_NUMBER)

answered Sep 01 '15 at 17:35

BLUEPIXY

Why didn't you write `#define S(x) #x` directly? – Nasr Sep 01 '15 at 17:38
@Nasr if `S(MY_NUMBER)` then you get `"MY_NUMBER"` – BLUEPIXY Sep 01 '15 at 17:40
@BLUEPIXY, this works, but I don't understand why? Can you explain a bit more on what that second S_(x) may be doing? – tarabyte Sep 01 '15 at 17:41
@tarabyte There is a need to call indirectly for make `MY_NUMBER` expand `3`. `#var` will stringified `var` to `"var"`. – BLUEPIXY Sep 01 '15 at 17:43

1 Answers1